Solid electrolyte-based photoelectrochemical cell for production of pure hydrogen peroxide solution, and method of fabricating same

ABSTRACT

Proposed are a photoelectrochemical cell for producing hydrogen peroxide, a method of fabricating the same, and a method of producing hydrogen peroxide using the photoelectrochemical cell. The photoelectrochemical cell includes a photoanode including a photocatalyst, a cathode, and a solid polymer electrolyte layer disposed between the photoanode and the cathode and including a solid polymer electrolyte. The photoelectrochemical cell is for use in the production of hydrogen peroxide, and can produce hydrogen peroxide with electric energy generated from solar energy without requiring the supply of external electric energy.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application Nos. 10-2021-0032841 and 10-2021-0074513, filed on Mar. 12, 2021 and Jun. 9, 2021, respectively, the entire contents of which is incorporated herein for all purposes by this reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates generally to a photoelectrochemical cell for producing hydrogen peroxide, a method of fabricating the same, and a method of producing hydrogen peroxide using the photoelectrochemical cell. More particularly, the present disclosure relates to a photoelectrochemical cell that produces hydrogen peroxide with electric energy generated from solar energy without requiring the supply of external electric energy by including a photoanode including a photocatalyst, a cathode, and a solid polymer electrolyte layer disposed between the photoanode and the cathode and including a solid polymer electrolyte; to a method of fabricating the same; and to a method of producing hydrogen peroxide using the photoelectrochemical cell.

Description of the Related Art

Hydrogen peroxide (H₂O₂) is a chemical compound widely used in chemical synthesis, cosmetics, medicines, pulp and paper production, and wastewater treatment. As an industrial production method of H₂O₂, a multi-step process including hydrogenation of anthraquinone with hydrogen (H₂) and oxidation by oxygen (O₂) in an organic solvent has recently been proposed. However, this process requires the supply of high energy and the use of noble metal catalysts, and results in generation of toxic solvent wastes, which is not desirable.

As an alternative production method, direct production of H₂O₂ from H₂ and O₂, which is low-cost and decentralized synthesis of H₂O₂ in a nearby area requiring H₂O₂, is being studied. However, this method has major problems in practical use, such as the low yield of H₂O₂, the need for H₂O₂ purification, and safety issues associated with handling potentially explosive H₂ and O₂ gases.

Therefore, there is a need for a novel environmentally friendly and simple method for H₂O₂ synthesis.

As an exemplary method, photoelectrochemical (PEC) synthesis via water oxidation and O₂ reduction has been proposed. This method employs the use of a photocatalyst and is being actively studied by using various photocatalysts that include metal oxides and carbon nitrides.

However, in a PEC system, H₂O₂ is synthesized at a very low concentration of a few millimolar, which hinders practical applications of the system.

An additional problem for practical applications of the PEC system is the need for a process for purifying the synthesized H₂O₂. The PEC system usually requires the use of a highly concentrated electrolyte (0.1 to 2 M), which requires an additional purification process for separating the synthesized H₂O₂ from the electrolyte. However, even if this purification process is performed, there is still difficulty in separating the synthesized H₂O₂.

The foregoing is intended merely to aid in the understanding of the background of the present disclosure, and is not intended to mean that the present disclosure falls within the purview of the related art that is already known to those skilled in the art.

SUMMARY OF THE INVENTION

Accordingly, the present disclosure has been made keeping in mind the above problems occurring in the related art, and an objective of the present disclosure is to provide a photoelectrochemical cell for producing hydrogen peroxide, the photoelectrochemical cell being capable of efficiently producing pure hydrogen peroxide free from an electrolyte, and a method of fabricating the same.

Another objective of the present disclosure is to provide a method of producing hydrogen peroxide with electric energy generated from solar energy using the photoelectrochemical cell without requiring the supply of external electric energy.

In order to achieve the above objectives, according to one aspect of the present disclosure, there is provided a photoelectrochemical cell for use in production of hydrogen peroxide, the photoelectrochemical cell including: a photoanode including a photocatalyst; a cathode; and a solid polymer electrolyte layer disposed between the photoanode and the cathode and including a solid polymer electrolyte.

Furthermore, the photocatalyst may include: a support including titanium dioxide (TiO₂); and a ruthenium oxide loaded on the support.

Furthermore, the photoanode may include 0.5 to 1 part by weight of the ruthenium oxide, with respect to 100 parts by weight of the photocatalyst.

Furthermore, the support may have any one form selected from the group consisting of a nanorod form, a nanoneedle form, a sphere form, and a cube form.

Furthermore, the support may have a nanorod form, and the nanorod-form support may have a length of 2 to 2.5 μm and a thickness of 40 to 50 nm.

Furthermore, the cathode may include a carbon material and a compound loaded on the carbon material and represented by Structural Formula 1 below,

wherein in Structural Formula 1,

R may be a hydrogen atom, a carboxyl group, a sulfonic acid group, an amino group, or a hydroxyl group.

Furthermore, the carbon material may include at least one selected from the group consisting of natural graphite, artificial graphite, a single-walled carbon nanotube (SWCNT), a double-walled carbon nanotube (DWCNT), a multi-walled carbon nanotube (MWCNT), carbon nanofiber (CNF), graphene oxide (GO), and carbon black.

Furthermore, the cathode may include 1 to 10 parts by weight of the compound represented by Structural Formula 1, with respect to 100 parts by weight of the carbon material.

Furthermore, the solid polymer electrolyte layer may include: a proton exchange membrane positioned to face the photoanode and including a cation exchange resin; an anion exchange membrane positioned to face the cathode and including an anion exchange resin; and a polymer bead positioned between the proton exchange membrane and the anion exchange membrane and including the solid polymer electrolyte.

Furthermore, the cation exchange resin may include Nafion.

Furthermore, the anion exchange resin may include a gel polystyrene crosslinked with divinylbenzene, the gel polystyrene including quaternary ammonium as the functional group.

According to another aspect of the present disclosure, there is provided a method of fabricating a photoelectrochemical cell, the method including the steps of: (a) fabricating a photoanode including a photocatalyst; (b) fabricating a cathode; and (c) forming a solid polymer electrolyte layer including a solid polymer electrolyte between the photoanode and the cathode.

Furthermore, step (a) may include the steps of: (a-1) applying a solution including a ruthenium precursor to a support including titanium dioxide; and (a-2) drying the support coated with the solution including the ruthenium precursor to fabricate the photoanode that includes the support including titanium dioxide (TiO₂) and the photocatalyst including ruthenium oxide loaded on the support.

Furthermore, the ruthenium precursor may include RuCl₃.

Furthermore, step (b) may include the steps of (b-1) mixing a precursor of a compound represented by Structural Formula 1 below with a carbon material to prepare a mixed solution, and (b-2) drying the mixed solution to fabricate the cathode including the carbon material on which the compound represented by the Structural Formula 1 is loaded,

wherein in Structural Formula 1,

R may be a hydrogen atom, a carboxyl group, a sulfonic acid group, an amino group, or a hydroxyl group.

Furthermore, step (c) may include the steps of: (c-1) positioning a proton exchange membrane including a cation exchange resin so as to face the photoanode; (c-2) positioning an anion exchange membrane including an anion exchange resin so as to face the cathode; and (c-3) positioning a polymer bead including the solid polymer electrolyte between the proton exchange membrane and the anion exchange membrane.

According to still another aspect of the present disclosure, there is provided a method of producing hydrogen peroxide, the method including the steps of: (1) providing a photoelectrochemical cell including a photoanode, a cathode, and a solid polymer electrolyte layer positioned between the photoanode and the cathode; (2) oxidizing water at the photoanode under light irradiation to generate electrons (e⁻), oxygen (O₂), and hydrogen ions (H⁺), and reacting the electrons (e⁻) with oxygen (O₂), and water at the cathode to generate active oxygen species and hydroxide ions (OH⁻); and (3) reacting the hydrogen ions (H⁺) with the active oxygen species in the solid polymer electrolyte layer to produce hydrogen peroxide (H₂O₂).

Furthermore, the active oxygen species may include a hydroperoxyl radical (HO₂.⁻) and a superoxide radical (O₂.⁻).

Furthermore, the method may produce hydrogen peroxide with electric energy generated from solar energy without requiring supply of external electric energy.

Furthermore, the method may further include the step of, after step (3), (4) adding water to the solid polymer electrolyte layer to dissolve the hydrogen peroxide to prepare an aqueous hydrogen peroxide solution, and discharging the prepared aqueous hydrogen peroxide solution from the solid polymer electrolyte layer to outside to obtain the aqueous hydrogen peroxide solution.

The photoelectrochemical cell according to the present disclosure can efficiently produce pure hydrogen peroxide in high yield.

In addition, the photoelectrochemical cell according to the present disclosure can produce hydrogen peroxide with electric energy generated from solar energy without requiring the supply of external electric energy.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate exemplary embodiments of the present disclosure and are not construed to limit any aspect of the disclosure.

FIG. 1 is a schematic diagram of a photoelectrochemical cell according to an embodiment of the present disclosure;

FIG. 2 is a graph illustrating a FT-IR measurement result of a cathode of Example 1, a cathode and anthraquinone of Comparative Example 2;

FIG. 3 is a graph illustrating a measurement result of cyclic voltammograms and Faradaic efficiencies of the cathode of Example 1 and a cathode of Comparative Example 3;

FIG. 4A is a graph illustrating the number of migrated electrons to the cathode of Example 1 and the cathode of Comparative Example 3;

FIG. 4B is a graph illustrating HO₂ ⁻ selectivity of the cathode of Example 1 and the cathode of Comparative Example 3;

FIG. 5A is a surface SEM image of a TiO₂ nanorod prepared in Preparation Example 1;

FIG. 5B is a sectional SEM image of the TiO₂ nanorod prepared in Preparation Example 1;

FIG. 5C is a surface SEM image of a photoanode fabricated in Example 1;

FIG. 6A is a graph illustrating XPS spectra of the photoanode of Example 1 and the TiO₂ nanorod of Preparation Example 1;

FIG. 6B is a graph illustrating XPS spectra of the photoanode of Example 1 and the TiO₂ nanorod of Preparation Example 1;

FIG. 6C is a graph illustrating an XRD measurement result of the photoanode of Example 1 and the TiO₂ nanorod of Preparation Example 1;

FIG. 6D is a graph illustrating a measurement result of absorbance of the photoanode of Example 1 and the TiO₂ nanorod of Preparation Example 1, analyzed using the Kubelka-Munk (K.M.) equation;

FIG. 7A is a graph illustrating a measurement result of the amount of photocurrent generation in a three-electrode system experiment using photoelectrochemical cells of Example 1 and Comparative Examples 3 to 5;

FIG. 7B is a graph illustrating a measurement result of the amount of hydrogen peroxide generation and Faradaic efficiency in the three-electrode system experiment using the photoelectrochemical cells of Example 1 and Comparative Examples 3 to 5;

FIG. 7C is a graph illustrating a measurement result of the amount of photocurrent generation in a two-electrode system experiment using the photoelectrochemical cells of Example 1 and Comparative Examples 3 to 5;

FIG. 7D is a graph illustrating a measurement result of photocurrent generation in the two-electrode system experiment under a bias-free condition using the photoelectrochemical cells of Example 1 and Comparative Examples 3 to 5;

FIG. 7E is a graph illustrating a measurement result of the amount of hydrogen peroxide generation and Faradaic efficiency in the two-electrode system experiment under a bias-free condition using the photoelectrochemical cells of Example 1 and Comparative Examples 3 to 5;

FIG. 7F is a graph illustrating a measurement result of the amount of hydrogen peroxide generation measured while changing a flow rate of deionized water supplied to a solid polymer electrolyte layer of Example 1;

FIG. 8A is a graph illustrating a measurement result of the amount of photocurrent generation in the three-electrode system and two-electrode system experiments using a photoelectrochemical cell of Example 2;

FIG. 8B is a graph illustrating a measurement result of the amount of photocurrent generation in the two-electrode experiment under a bias-free condition using the photoelectrochemical cell of Example 2;

FIG. 8C is a graph illustrating a measurement result of the amount of hydrogen peroxide generation measured while changing a flow rate of deionized water supplied to a solid polymer electrolyte layer of Example 2;

FIG. 9 is a graph illustrating a measurement result of the amount of photocurrent generation and hydrogen peroxide concentration generated while operating the photoelectrochemical cell of Example 2 for 100 hours;

FIG. 10 is a surface SEM image of a photoanode after the experiment of FIG. 9;

FIG. 11A is a graph illustrating a measurement result of photocurrent generation of photoelectrochemical cells of Example 1 and Comparative Example 6; and

FIG. 11B is a graph illustrating photocurrent-time profiles of the photoelectrochemical cells of Example 1 and Comparative Example 6.

DETAILED DESCRIPTION OF THE INVENTION

Hereinbelow, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings such that the disclosure can be easily embodied by one of ordinary skill in the art to which this disclosure belongs.

However, the following description is not intended to limit the present disclosure to those exemplary embodiments. Further, when it is determined that the detailed description of the known art related to the present disclosure might obscure the gist of the present disclosure, the detailed description thereof will be omitted.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be understood that the terms “comprises” or “have” used in this specification, specify the presence of stated features, processes, operations, components, parts, or a combination thereof, but do not preclude the presence or addition of one or more other features, numerals, processes, operations, components, parts, or a combination thereof.

It will be further understood that, although the terms “first”, “second”, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments of the present disclosure.

Further, it will be understood that when an element is referred to as being “formed” or “layered” on another element, it can be formed or layered so as to be directly attached to the entire surface or one surface of the other element, or intervening elements may be present therebetween.

Hereinafter, a photoelectrochemical cell for producing hydrogen peroxide, a method of fabricating the same, and a method of producing hydrogen peroxide using the photoelectrochemical cell will be described in detail. However, these are for illustrative purposes, and the present disclosure is not limited thereby. The present disclosure is only defined by the scope of the claims which will be described later.

FIG. 1 is a schematic diagram of a photoelectrochemical cell according to an embodiment of the present disclosure.

Referring to FIG. 1, the present disclosure provides a photoelectrochemical cell for use in production of hydrogen peroxide. The photoelectrochemical cell includes a photoanode including a photocatalyst; a cathode; and a solid polymer electrolyte layer disposed between the photoanode and the cathode and including a solid polymer electrolyte.

In addition, the photocatalyst may include a support including titanium dioxide (TiO₂) and ruthenium oxide loaded on the support.

The ruthenium oxide may be RuO_(x), where x is any one of integers of 2 to 5, preferably 2.

When the ruthenium oxide is used as an active material in the photocatalyst, the ruthenium oxide oxidizes water on the surface of the photoanode to generate oxygen (O₂) and hydrogen ions (H⁺), and is different from Pt or Pd that directly generates hydrogen peroxide through a catalytic reaction.

The photocatalyst may have a specific surface area of 1 to 2 cm². This specific surface area is a BET specific surface area. When the specific surface area of the photocatalyst is included in the above range, this is desirable because the amount of current generation can be increased, thereby effectively producing highly concentrated hydrogen peroxide.

In addition, as a result of XPS measurement, the photocatalyst may have a peak at a binding energy of 280.8 eV to 464.0 eV and a binding energy of 486.1 eV. When the photocatalyst shows a peak in this range, this means that the ruthenium oxide is loaded on the titanium dioxide.

In the photocatalyst, the ruthenium oxide may be amorphous, and the amorphous ruthenium oxide is desirable because it can oxidize water more effectively than crystalline ruthenium oxide.

In addition, the photoanode may include 0.5 to 1 part by weight of the ruthenium oxide, with respect to 100 parts by weight of the photocatalyst.

In addition, the support may have any one form selected from the group consisting of a nanorod form, a nanoneedle form, a sphere form, and a cube form, preferably, a nanorod form.

In addition, the nanorod-form support may have a length of 2 to 2.5 μm and a thickness of 40 to 50 nm.

The photocatalyst has a structure in which the ruthenium oxide is loaded, e.g., deposited, on the titanium dioxide support, and thus may have a needle-like form.

In addition, the cathode may include a carbon material and a compound loaded on the carbon material and represented by Structural Formula 1 below.

In Structural Formula 1,

R is a hydrogen atom, a carboxyl group, a sulfonic acid group, an amino group, or a hydroxyl group.

In addition, the carbon material may include at least one selected from the group consisting of natural graphite, artificial graphite, a single-walled carbon nanotube (SWCNT), a double-walled carbon nanotube (DWCNT), a multi-walled carbon nanotube (MWCNT), carbon nanofiber (CNF), graphene oxide (GO), and carbon black, preferably at least one selected from the group consisting of graphite and artificial graphite.

In addition, the cathode may include 1 to 10 parts by weight of the compound represented by Structural Formula 1, with respect to 100 parts by weight of the carbon material.

In addition, the solid polymer electrolyte layer may include a proton exchange membrane positioned to face the photoanode and including a cation exchange resin; an anion exchange membrane positioned to face the cathode and including an anion exchange resin, and a polymer bead positioned between the proton exchange membrane and the anion exchange membrane and including the solid polymer electrolyte.

In addition, the cation exchange resin may include Nafion.

In addition, the anion exchange resin may include a gel polystyrene crosslinked with divinylbenzene, the gel polystyrene including quaternary ammonium as the functional group.

The proton exchange membrane may selectively migrate H⁺ ions generated at the photoanode, and the anion exchange membrane may selectively migrate HO₂ ⁻ ions generated at the cathode.

The photoelectrochemical cell may form a three-electrode system by adding a counter electrode to the photoanode and the cathode.

The photoelectrochemical cell may form a two-electrode system by directly connecting the photoanode and the cathode to each other.

The present disclosure provides a method of fabricating a photoelectrochemical cell. The method includes the steps of: (a) fabricating a photoanode including a photocatalyst; (b) fabricating a cathode; and (c) forming a solid polymer electrolyte layer including a solid polymer electrolyte between the photoanode and the cathode.

First, the Photoanode Including the Photocatalyst is Fabricated (Step (a)).

Step (a) may be performed by two steps.

First, a solution including a ruthenium precursor is applied to a support including titanium dioxide (step (a-1)).

The ruthenium precursor may include RuCl₂.

Next, the support coated with the solution including the ruthenium precursor is dried to fabricate the photoanode including the support including titanium dioxide (TiO₂) and the photocatalyst including ruthenium oxide loaded on the support (step (a-2)).

Next, the Cathode is Fabricated (Step (b)).

Step (b) may be performed by two steps.

First, a precursor of a compound represented by Structural Formula 1 below and a carbon material are mixed to prepare a mixed solution (step (b-1))

In Structural Formula 1,

R is a hydrogen atom, a carboxyl group, a sulfonic acid group, an amino group, or a hydroxyl group.

The precursor of the compound represented by Structural Formula 1 may include at least one selected from the group consisting of anthraquinone-2-carboxylic acid, anthraquinone, anthraquinone-2-sulfonic acid, 2-aminoanthraquinone, and 2-hydroxyanthraquinone, preferably at least one selected from the group consisting of anthraquinone-2-carboxylic acid, anthraquinone, and anthraquinone-2-sulfonic acid, and more preferably anthraquinone-2-carboxylic acid.

The carbon material may include at least one selected from the group consisting of natural graphite, artificial graphite, a single-walled carbon nanotube (SWCNT), a double-walled carbon nanotube (DWCNT), a multi-walled carbon nanotube (MWCNT), carbon nanofiber (CNF), graphene oxide (GO), and carbon black, preferably at least one selected from the group consisting of graphite and artificial graphite.

Next, the mixed solution is dried to fabricate the cathode including the carbon material on which the compound represented by Structural Formula 1 is loaded (step (b-2)).

Finally, the Solid Polymer Electrolyte Layer Including the Solid Polymer Electrolyte is Formed Between the Photoanode and the Cathode (Step (c)).

Step (c) may be performed by three steps.

First, a proton exchange membrane including a cation exchange resin is positioned to face the photoanode (step (c-1)).

Next, an anion exchange membrane including an anion exchange resin is positioned to face the cathode (step (c-2)).

Finally, a polymer bead including the solid polymer electrolyte is positioned between the proton exchange membrane and the anion exchange membrane (step (c-3)).

The present disclosure provides a method of producing hydrogen peroxide. The method includes the steps of: (1) providing a photoelectrochemical cell including a photoanode, a cathode, and a solid polymer electrolyte layer positioned between the photoanode and the cathode; (2) oxidizing water at the photoanode under light irradiation to generate electrons (e⁻), oxygen (O₂), and hydrogen ions (H⁺), and reacting the electrons (e⁻) with oxygen (O₂), and water at the cathode to generate active oxygen species and hydroxide ions (OH⁻); and (3) reacting the hydrogen ions (H⁺) with the active oxygen species in the solid polymer electrolyte layer to produce hydrogen peroxide (H₂O₂).

In addition, the active oxygen species may include at least one selected from the group consisting of a hydroperoxyl radical (HO₂.⁻) and a superoxide radical (O₂.⁻).

In addition, the method of producing hydrogen peroxide can produce hydrogen peroxide with electric energy generated from solar energy without requiring the supply of external electric energy.

In addition, the method of producing hydrogen peroxide may include the step of, after step (3), (4) adding water to the solid polymer electrolyte layer to dissolve the hydrogen peroxide to prepare an aqueous hydrogen peroxide solution, and discharging the prepared aqueous hydrogen peroxide solution from the solid polymer electrolyte layer to outside to obtain the aqueous hydrogen peroxide solution.

EXAMPLE

Hereinafter, examples of the present disclosure will be described. However, these examples are for illustrative purposes, and the scope of the present disclosure is not limited thereby.

Preparation of Support Including Titanium Dioxide Preparation Example 1

Two pieces of FTO slides (1 cm×1 cm) were placed vertically in a Teflon-lined stainless steel autoclave (total 100 mL volume) including 25 mL HCl (Aldrich, 37%), 1 mL titanium(IV) butoxide (Aldrich, 97%) and 25 mL deionized (DI) water while conductive sides of fluorine-doped tin oxide (FTO, Pilkington, 15 Ω/m, hereafter referred to as “FTO”) faced the wall. The autoclave was placed in an oven pre-heated to 170° C. for 6 hours, and then cooled to room temperature.

The resultant product was rinsed with deionized water and dried in air, followed by annealing by a hydrothermal method at 550° C. for 1 hour with a ramping rate of 10° C./min to prepare a TiO₂ nanorod (hereinafter referred to as “TNR”) with a specific surface area of 1 cm². The prepared nanorod had a width of 40 to 50 nm and a length of 2 to 3 μm.

Preparation Example 2

A TiO₂ nanorod with a specific surface area of 4 cm² was prepared in the same manner as in Preparation Example 1, except that two pieces of FTO slides with a size of 2 cm×2 cm were used instead of the two pieces of FTO slides with a size of 1 cm×1 cm. The prepared nanorod had a width of 40 to 50 nm and a length of 2 to 3 μm.

Fabrication of Photoelectrochemical Cell Example 1

FIG. 1 is a schematic diagram of a photoelectrochemical cell according to an embodiment of the present disclosure. Example 1 was fabricated with reference to FIG. 1.

For photoelectrochemical synthesis of hydrogen peroxide, a 3-compartment-stack system composed of an anode compartment, a middle compartment, and a cathode compartment was used to combine water oxidation reaction (WOR) and oxygen reduction reaction (ORR).

(Fabrication of Photoanode)

10 μL/cm² of a RuCl₃ (10 nM, Aldrich, 99.98%) ethanol (J.T. Baker, 99.9%) solution was drop-cast onto the TiO₂ nanorod (hereinafter referred to as “TNR”) with a specific surface area of 1 cm² prepared according to Preparation Example 1. After drying the TNR in air for 30 minutes at room temperature, the resultant product was immersed in a 0.1 M KOH solution for 1 minute. According to this process, RuO_(x) was prepared, with the result that a photoanode including RuO_(x) (0<x≤2)-deposited TNR (hereinafter referred to as “RuO_(x)/TNR”) photocatalyst (needle-like form) was fabricated. In the photocatalyst, the amount of RuO_(x) was 0.5 parts by weight with respect to 100 parts by weight of the photocatalyst.

Thereafter, the photoanode was placed in the anode compartment, and a 1 M H₂SO₄ solution was added.

(Fabrication of Cathode)

A graphite rod (Aldrich, diameter 6 mm, 99.995%) was immersed in anthraquinone-2-carboxylic acid (AQ-2-COOH, 3 mM, Aldrich, 98%), and dried in air at room temperature to fabricate an anthraquinone-loaded graphite rod (AQ/G) cathode. In the graphite rod on which anthraquinone was loaded, the amount of anthraquinone was 10 parts by weight with respect to 100 parts by weight of the graphite rod on which anthraquinone was loaded.

Thereafter, the cathode was placed in the cathode compartment, and a 1 M H₂SO₄ solution purged with oxygen was added.

(Formation of Solid Polymer Electrolyte Layer)

As a solid polymer electrolyte, polystyrene microspheres (Aldrich, size 6.0 to 10.0 μm) crosslinked with divinylbenzene were used. Specifically, the middle compartment was filled with the polystyrene microspheres crosslinked with divinylbenzene to form the solid polymer electrolyte.

A proton exchange membrane (PEM, Nafion membrane N117) was placed between the middle compartment and the anode compartment, and an anion exchange membrane (AEM, AMI-70015, Membrane International) was placed between the middle compartment and the cathode compartment to form a solid polymer electrolyte layer.

The solid polymer electrolyte layer (middle compartment) allowed deionized water (DI water) to flow therethrough.

Example 2

A photoelectrochemical cell was fabricated in the same manner as in Example 1, except that in fabricating a photoanode, a TiO₂ nanorod with a specific surface area of 4 cm² prepared according to Preparation Example 2 was used instead of the TiO₂ nanorod with a specific surface area of 1 cm² prepared according to Preparation Example 1.

Comparative Example 1

A photoelectrochemical cell was fabricated in the same manner as in Example 1, except that a solution including 4 mM FeCl2 and 6 mM NiCl2 in ethanol was used to fabricate a FeNiO_(x)/TNR photoanode, instead of a RuCl₃ ethanol solution used to fabricate a RuO_(x)/TNR photoanode.

Comparative Example 2

A photoelectrochemical cell was fabricated in the same manner as in Example 1, except that a solution including 10 mM CoCl₂ in ethanol was used to fabricate a CoO_(x)/TNR photoanode, instead of a RuCl₃ ethanol solution used to fabricate a RuO_(x)/TNR photoanode.

Comparative Example 3

A photoelectrochemical cell was fabricated in the same manner as in Example 1, except that a graphite rod (Aldrich, diameter 6 mm, 99.995%) was used as a cathode instead of an anthraquinone-loaded graphite rod (AQ/G) cathode.

Comparative Example 4

A photoelectrochemical cell was fabricated in the same manner as in Example 1, except that a TiO₂ nanorod with a specific surface area of 1 cm² prepared according to Preparation Example 1 was used as a photoanode instead of a RuO_(x)/TNR photoanode.

Comparative Example 5

A photoelectrochemical cell was fabricated in the same manner as in Example 1, except that a TiO₂ nanorod with a specific surface area of 1 cm² prepared according to Preparation Example 1 was used as a photoanode instead of a RuO_(x)/TNR photoanode, and a graphite rod (Aldrich, diameter 6 mm, 99.995%) was used as a cathode instead of an anthraquinone-loaded graphite rod (AQ/G) cathode.

Comparative Example 6

A photoelectrochemical cell was fabricated in the same manner as in Example 1, except that a TiO₂ nanorod with a specific surface area of 1 cm² prepared according to Preparation Example 1 was used as a photoanode instead of a RuO_(x)/TNR photoanode, and a polyethylene film separator was used instead of a solid polymer electrolyte (polystyrene crosslinked with divinylbenzene microspheres).

EXPERIMENTAL EXAMPLE Experimental Example 1: Fourier Transform Infrared (FT-IR) Measurement

FIG. 2 is a graph illustrating a FT-IR measurement result of the cathode of Example 1, a cathode and anthraquinone of Comparative Example 2.

Specifically, the anthraquinone-loaded graphite rod cathode fabricated according to Example 1 and a graphite rod cathode used in Comparative Example 2 were ground in a mortar. Then, FT-IR was measured using an attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR; Thermo Scientific iS50, a scan number of 100, using ZeSe), and the results are illustrated as AQ/G and G in FIG. 2, respectively. In addition, FT-IR of anthraquinone was measured for reference. For comparison, obtained peak intensity was reduced to 1/30, and the results are illustrated as AQ powder in FIG. 2.

Referring to FIG. 2, the anthraquinone-loaded graphite rod prepared according to Example 1 exhibited apparent peaks at 696 cm⁻¹, 1267 cm⁻¹, 1666 cm⁻¹, and 1701 cm⁻¹, while the graphite rod used in Comparative Example 2 exhibited no peaks. This result indicates that anthraquinone was loaded (anchored) on the graphite rod by a solution immersion process of Example 1.

Experimental Example 2: Evaluation of Cyclic Voltammogram and Faradaic Efficiency of Cathode

FIG. 3 is a graph illustrating a measurement result of cyclic voltammograms and Faradaic efficiencies of the cathode of Example 1 and a cathode of Comparative Example 3.

Specifically, the cyclic voltammograms were measured for the cathode of Example 1 and the cathode of Comparative Example 3. In this case, the cathode was used as a working electrode, Pt foil was used as a counter electrode, and Hg/HgO was used as a reference electrode. The cyclic voltammograms were measured in the range of 0.06 to −1.06 V at a scan rate of 50 mVs⁻¹ in the dark while adding 1M KOH to the working electrode and purging Ar (purity 99.9%) into KOH for 30 minutes before the measurement. The amount of photocurrent generation was measured and the results are illustrated in FIG. 3. In addition, the amount of photocurrent generation was measured under the same conditions while purging O₂ (99.9%) instead of Ar, and the results are also illustrated in FIG. 3.

In addition, 0.50 mL of a sample was mixed with 1.40 mL of deionized water, 0.75 mL of a C₈H₅KO₄ (0.1 M potassium biphthalate, Alfa Aesar, 98%) solution, and 0.75 mL of a KI solution (0.4 M) including NaOH (0.06 M) and (NH₄)₂MoO₄ (10⁻⁴ M, Aldrich, 99%), and stirred vigorously for 2 minutes to prepare a solution. 0.10 mL HCl (1 M, Aldrich, 99.5%) were added to the above solution. For the resultant product, absorbance was measured at 372 nm using a UV/Visible spectrophotometer (Libra S22, Biochrom), and for generated HO₂ ⁻, Faradaic efficiency was measured. The results are illustrated in FIG. 3.

The Faradaic efficiency was calculated using the following: Fe=(2Fn/Q_(ph))×100 (where F is the Faraday constant, n is the measured amount of HO₂ ⁻ (mol), and Q_(ph) is the integrated photocharge).

Referring to FIG. 3, it can be seen that the anthraquinone-anchored graphite rod cathode of Example 1 exhibited a superior photocurrent generation and a superior Faradaic efficiency to the graphite rod cathode of Comparative Example 3.

Experimental Example 3: Evaluation of Rotating Ring-Disk Electrode (RRDE) Voltammogram of Cathode

FIG. 4A is a graph illustrating the number of migrated electrons to the cathode of Example 1 and the cathode of Comparative Example 3, and FIG. 4B is a graph illustrating HO₂ ⁻ selectivity of the cathode of Example 1 and the cathode of Comparative Example 3.

Specifically, the anthraquinone-anchored graphite rod cathode of Example 1 and the graphite rod cathode of Comparative Example 3 were ground in a mortar to prepare fine powder, and 30 mg of the powder and 12 μL of a Nafion solution (Aldrich, 5% by weight in a mixture of ethanol and water (40%)) were dissolved in 1 mL of ethanol and well dispersed by sonication for 30 minutes. A 5 μL aliquot of the resultant product was drop-cast onto a glassy carbon disk and dried at room temperature for 10 minutes. The drop-casting and drying processes were each repeated 3 times to fabricate a glassy carbon working electrode.

For measurement of electrochemical rotating ring-disk electrode voltammograms, a Pt ring/glassy carbon disk working electrode (ring OD 7 mm/ID 5 mm, disk ID 4 mm, ALS Co., no. 012613), a Pt wire counter electrode, and a Ag/AgCl reference electrode were placed in a single cell containing 0.1 M KOH (pH 13). The cell was mounted on a rotating ring disk electrode rotator (RRDE-3A, ALS Co., Ltd), and the rotation speed was varied from 100 to 1600 revolutions per minute (rpm). From the measured results, the number of migrated electrons (n) to the cathode and HO₂ ⁻ selectivity were measured using Equations 1 and 2 below, and the results are illustrated in FIGS. 4A and 4B, respectively.

$\begin{matrix} {n = \left. \frac{4 \times I_{Disk}}{I_{Disk} + \frac{I_{Ring}}{N}}↵ \right.} & \left\lbrack {{Equation}1} \right\rbrack \end{matrix}$ $\begin{matrix} {{\%\left( {HO}_{2}^{-} \right)} = \frac{200 \times \frac{I_{Ring}}{N}}{I_{Disk} + \frac{I_{Ring}}{N}}} & \left\lbrack {{Equation}2} \right\rbrack \end{matrix}$

(In Equations 1 and 2, I_(Disk) is the disk current, I_(Ring) is the ring current, and N is the current collection efficiency (0.424) of the Pt ring)

Referring to FIGS. 4A and 4B, it can be seen that the anthraquinone-anchored graphite rod cathode of Example 1 exhibited a superior number of migrated electrons and a superior HO₂ ⁻ selectivity to the graphite rod cathode of Comparative Example 3.

Experimental Example 4: SEM Evaluation

FIG. 5A is a surface SEM image of the TiO₂ nanorod prepared in Preparation Example 1. FIG. 5B is a sectional SEM image of the TiO₂ nanorod prepared in Preparation Example 1.

Specifically, the surface SEM image and the sectional SEM image of the TiO₂ nanorod prepared in Preparation Example 1 were obtained using high resolution field emission scanning electron microscopy (FE-SEM, JOEL JSM-7800F PRIME) with dual energy dispersive X-ray spectroscopy, and are illustrated in FIGS. 5A and 5B, respectively.

Referring to FIGS. 5A and 5B, it can be seen that the TiO₂ nanorod had a rectangular bunched morphology with a width of about 50 nm and a length of about 2.3 μm.

FIG. 5C is a surface SEM image of the photoanode fabricated in Example 1.

Referring to FIG. 5C, it can be seen that RuO_(x) loaded on the TiO₂ nanorod caused a change in morphology, resulting in a needle-like structure.

Experimental Example 5: X-Ray Photoelectron Spectroscopy (XPS) and X-Ray Diffraction (XRD) Evaluation

FIGS. 6A and 6B are graphs each illustrating XPS spectra of the photoanode of Example 1 and the TiO₂ nanorod of Preparation Example 1.

Specifically, the XPS spectra of the photoanode fabricated in Example 1 (RuO_(x)/TNR in FIGS. 6A and 6B) and the TiO₂ nanorod prepared in Preparation Example 1 (TNR in FIGS. 6A and 6B) were measured using monochromated Al Kα radiation as an X-ray source (1486.6 eV). The results are illustrated in FIGS. 6A and 6B.

Referring to FIGS. 6A and 6B, the photoanode fabricated in Example 1 exhibited Ru-related peaks, particularly Ru 3d_(5/2) and Ru 3p peaks, indicating that Ru was present on the surface of the TiO₂ nanorod. On the other hand, the TiO₂ nanorod prepared in Preparation Example 1 exhibited no Ru-related peaks such as Ru 3d_(5/2) and Ru 3p peaks. In FIG. 6A, the peak at a binding energy of about 285 eV was a Ru 3d_(3/2) or C is peak, and the TiO₂ nanorod exhibited the C is peak.

Referring to FIG. 6B, it can be seen that a Ti 2p peak for the photoanode fabricated in Example 1 shifted to a higher binding energy than the TiO₂ nanorod, indicating that an interaction between RuO_(x) and TiO₂ occurred.

FIG. 6C is a graph illustrating an XRD measurement result of the photoanode of Example 1 and the TiO₂ nanorod of Preparation Example 1.

Referring to FIG. 6C, it can be seen that the photoanode and the TiO₂ nanorod exhibited the same rutile TiO₂ peaks with the predominant (101) plane at 2Θ=36.8°, indicating that the loading of RuO_(x) did not affect the crystalline phase of TiO₂. Therefore, there were no additional peaks associated with RuO_(x) loaded on the TiO₂ nanorod, indicating that the RuO_(x) phase remained amorphous.

FIG. 6D is a graph illustrating a measurement result of absorbance of the photoanode of Example 1 and the TiO₂ nanorod of Preparation Example 1, analyzed using the Kubelka-Munk (K.M.) equation. The Kubelka-Munk (K.M.) equation is as Equation 3 below.

Kubelka-Munk (K.M.)=1−R ²/2R  [Equation 3]

(In Equation 3, R is absorbance)

Referring to FIG. 6D, it can be seen that the loading of RuO_(x) did not significantly affect the optical properties of the TiO₂ nanorod.

Experimental Example 6: Evaluation of Photoelectrochemical Properties

The photoelectrochemical properties of the photoelectrochemical cells fabricated according to Example 1 and Comparative Examples 3 to 5 were measured using linear sweep voltammetry (LSV) under solar simulating conditions. This experiment was conducted with a three-electrode system and a two-electrode system each using each of the photoelectrochemical cells as a working electrode. A three-electrode system experiment used Pt foil and Ag/AgCl as a counter electrode and a reference electrode, respectively, while a two-electrode system experiment used no reference electrode. For these experiments, an electrochemical workstation (VersaSTAT 3-400, Princeton Applied Research) was used.

The linear sweep voltammetry was conducted in the range of −0.20 to +1.80 V (vs. Ag/AgCl) at a scan rate of 50 mVs⁻¹ in the dark under simulated sunlight (AM 1.5G, 100 mWcm⁻²) while supplying deionized water to a solid polymer electrolyte layer (middle compartment) of the photoelectrochemical cell at a flow rate of 30 mL/h, and the amount of photocurrent generation was measured.

FIG. 7A is a graph illustrating a measurement result of the amount of photocurrent generation in the three-electrode system experiment using the photoelectrochemical cells of Example 1 and Comparative Examples 3 to 5.

Referring to FIG. 7A, it can be seen that the photoelectrochemical cell of Example 1 generated more photocurrent than those of Comparative Examples 3 to 5, indicating that the photoanode and the cathode of Example 1 exhibited excellent photoelectrochemical properties.

FIG. 7B is a graph illustrating a measurement result of the amount of hydrogen peroxide generation and Faradaic efficiency in the three-electrode system experiment using the photoelectrochemical cells of Example 1 and Comparative Examples 3 to 5.

Referring to FIG. 7B, it can be seen that the photoelectrochemical cell of Example 1 generated H₂O₂ at a high concentration of about 0.8 mM, and exhibited an excellent Faradaic efficiency of about 90%. On the other hand, the photoelectrochemical cells of Comparative Examples 3 to 5 exhibited a lower H₂O₂ concentration and a lower Faradaic efficiency than the photoelectrochemical cell of Example 1.

FIG. 7C is a graph illustrating a measurement result of the amount of photocurrent generation in the two-electrode system experiment using the photoelectrochemical cells of Example 1 and Comparative Examples 3 to 5, and FIG. 7D is a graph illustrating a measurement result of photocurrent generation in the two-electrode system experiment under a bias-free condition using the photoelectrochemical cells of Example 1 and Comparative Examples 3 to 5. Specifically, for the two-electrode system, the measurement was conducted by directly applying a potential (cell voltage (E_(cell))) between the photoanode and the cathode.

Referring to FIG. 7C, it can be seen that the photoelectrochemical cell of Example 1 generated a very higher photocurrent than the photoelectrochemical cells of Comparative Examples 3 to 5.

In addition, referring to FIG. 7D, it can be seen that the photoelectrochemical cell of Example 1 generated a photocurrent even under a bias-free condition (E_(cell)=0.0 V).

FIG. 7E is a graph illustrating a measurement result of the amount of hydrogen peroxide generation and Faradaic efficiency in the two-electrode system experiment under the bias-free condition (the condition in which deionized water is supplied to a solid polymer electrolyte layer (middle compartment) at a flow rate of 30 mL/h) using the photoelectrochemical cells of Example 1 and Comparative Examples 3 to 5.

Referring to FIG. 7E, it can be seen that the photoelectrochemical cell of Example 1 generated H₂O₂ at a very high concentration of about 0.7 mM, and exhibited an excellent Faradaic efficiency of about 90%. On the other hand, the photoelectrochemical cells of Comparative Examples 3 to 5 exhibited a lower H₂O₂ concentration and a lower Faradaic efficiency than the photoelectrochemical cell of Example 1.

FIG. 7F is a graph illustrating a measurement result of the amount of hydrogen peroxide generation measured while changing a flow rate of deionized water supplied to a solid polymer electrolyte layer of Example 1.

Referring to FIG. 7F, it can be seen that when deionized water was supplied at a flow rate of 0.8 mL/h, H₂O₂ was generated at the highest concentration of about 30 mM.

FIG. 8A is a graph illustrating a measurement result of the amount of photocurrent generation in the three-electrode system and two-electrode system experiments using the photoelectrochemical cell of Example 2. Specifically, as similar to the case of Example 1, the amount of photocurrent generation was measured in the three-electrode system and the two-electrode system using linear sweep voltammetry (LSV) under solar simulating irradiation.

FIG. 8B is a graph illustrating a measurement result of the amount of photocurrent generation in the two-electrode experiment under a bias-free condition using the photoelectrochemical cell of Example 2.

Referring to FIGS. 8A and 8B, it can be seen that both the three-electrode system and the two-electrode system using the photoelectrochemical cell of Example 2 exhibited a very high amount of photocurrent generation.

FIG. 8C is a graph illustrating a measurement result of the amount of hydrogen peroxide generation measured while changing a flow rate of deionized water supplied to a solid polymer electrolyte layer of Example 2.

Referring to FIG. 8C, it can be seen that when deionized water was supplied at a flow rate of 0.8 mL/h for 1 hour, H₂O₂ was generated at the highest concentration of about 80 mM.

Experimental Example 7: Evaluation of Life Characteristics

FIG. 9 is a graph illustrating a measurement result of the amount of photocurrent generation and hydrogen peroxide concentration generated while operating the photoelectrochemical cell of Example 2 for 100 hours. Specifically, for the two-electrode system of the photoelectrochemical cell fabricated according to Example 2, the amount of photocurrent generation and H₂O₂ concentration were measured under a bias-free condition while supplying deionized water at a flow rate of 0.8 mL/h for 100 hours, and the results are illustrated in FIG. 9.

Referring to FIG. 9, it can be seen that the photoelectrochemical cell of Example 2 generated H₂O₂ at a concentration of about 80 mM while stably maintaining a photocurrent of about 3 mA even after operation for 100 hours.

This result indicates that the photoelectrochemical cell according to the present disclosure could generate very highly concentrated H₂O₂ even using only sunlight.

FIG. 10 is a surface SEM image of a photoanode after the measurement of the amount of photocurrent generation and hydrogen peroxide concentration generated while operating the photoelectrochemical cell of Example 2 for 100 hours.

Referring to FIG. 10, it can be seen that the photoelectrochemical cell of Example 2 did not undergo corrosion even after operation for 100 hours.

Experimental Example 8: Characteristic Evaluation with or without Presence of Solid Electrolyte

FIG. 11A is a graph illustrating a measurement result of photocurrent generation of the photoelectrochemical cells of Example 1 and Comparative Example 6, and FIG. 11B is a graph illustrating photocurrent-time profiles of the photoelectrochemical cells of Example 1 and Comparative Example 6.

Specifically, the photoelectrochemical properties of the photoelectrochemical cells of Example 1 and Comparative Example 6 were measured using linear sweep voltammetry (LSV), and the photocurrent time-profiles were measured and the results are illustrated in FIGS. 11A and 11B, respectively.

The linear sweep voltammetry was conducted in the range of −0.20 to +1.80 V (vs. Ag/AgCl) at a scan rate of 50 mVs⁻¹ in the dark under simulated sunlight (AM 1.5G, 100 mWcm⁻²) while supplying deionized water to a solid polymer electrolyte layer (middle compartment) of the photoelectrochemical cell at a flow rate of 30 mL/h, and the amount of photocurrent generation was measured.

The photocurrent time-profiles were measured in the range of +1.30 V (vs. Ag/AgCl) under simulated sunlight (AM 1.5G, 100 mWcm⁻²) while supplying deionized water to a solid polymer electrolyte layer (middle compartment) of the photoelectrochemical cell at a flow rate of 30 mL/h.

Referring to FIG. 11A, it can be seen that Example 1 with the solid polymer electrolyte layer exhibited a higher amount of photocurrent generation than Comparative Example 6 without the solid polymer electrolyte layer even under the condition in which the same photoanodes and the same cathodes were used.

Referring to FIG. 11B, it can be seen that in Example 1 uniform and stable photocurrent was generated over time, while in Comparative Example 6, unstable photocurrent was generated. This is believed to be due to the change in pH in the anode and cathode compartments as H₂SO₄ and KOH in the anode and cathode compartments leaked into the middle compartment in the case of the absence of the solid polymer electrolyte layer.

Table 1 illustrates a measurement result of pH in the anode compartment, the middle compartment, and the cathode compartment in each of the photoelectrochemical cells of Example 1 and Comparative Example 6.

TABLE 1 Example 1 Comparative Example 6 Anode compartment 0.15 0.19 Middle compartment 6.80 10.90 Cathode compartment 13.60 13.40

Referring to Table 1, it can be clearly seen that in Example 1, the pH of the middle compartment was maintained neutral, while in Comparative Example 6, the pH of the middle compartment was alkaline.

The scope of the present disclosure is defined by the accompanying claims rather than the description which is presented above. Moreover, the present disclosure is intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents, and other embodiments that may be included within the spirit and scope of the present disclosure as defined by the appended claims. 

What is claimed is:
 1. A photoelectrochemical cell for use in production of hydrogen peroxide, the photoelectrochemical cell comprising: a photoanode comprising a photocatalyst; a cathode; and a solid polymer electrolyte layer disposed between the photoanode and the cathode and comprising a solid polymer electrolyte.
 2. The photoelectrochemical cell of claim 1, wherein the photocatalyst comprises: a support comprising titanium dioxide (TiO₂); and a ruthenium oxide loaded on the support.
 3. The photoelectrochemical cell of claim 2, wherein the photoanode comprises 0.5 to 1 part by weight of the ruthenium oxide, with respect to 100 parts by weight of the photocatalyst.
 4. The photoelectrochemical cell of claim 2, wherein the support has any one form selected from the group consisting of a nanorod form, a nanoneedle form, a sphere form, and a cube form.
 5. The photoelectrochemical cell of claim 4, wherein the support has a nanorod form, and the nanorod-form support has a length of 2 to 2.5 μm and a thickness of 40 to 50 nm.
 6. The photoelectrochemical cell of claim 1, wherein the cathode comprises a carbon material and a compound loaded on the carbon material and represented by Structural Formula 1 below,

wherein in Structural Formula 1, R is a hydrogen atom, a carboxyl group, a sulfonic acid group, an amino group, or a hydroxyl group.
 7. The photoelectrochemical cell of claim 6, wherein the carbon material comprises at least one selected from the group consisting of natural graphite, artificial graphite, a single-walled carbon nanotube (SWCNT), a double-walled carbon nanotube (DWCNT), a multi-walled carbon nanotube (MWCNT), carbon nanofiber (CNF), graphene oxide (GO), and carbon black.
 8. The photoelectrochemical cell of claim 6, wherein the cathode comprises 1 to 10 parts by weight of the compound represented by Structural Formula 1, with respect to 100 parts by weight of the carbon material.
 9. The photoelectrochemical cell of claim 1, wherein the solid polymer electrolyte layer comprises: a proton exchange membrane positioned to face the photoanode and comprising a cation exchange resin; an anion exchange membrane positioned to face the cathode and comprising an anion exchange resin; and a polymer bead positioned between the proton exchange membrane and the anion exchange membrane and comprising the solid polymer electrolyte.
 10. The photoelectrochemical cell of claim 9, wherein the cation exchange resin comprises Nafion.
 11. The photoelectrochemical cell of claim 9, wherein the anion exchange resin comprises a gel polystyrene crosslinked with divinylbenzene, the gel polystyrene comprising quaternary ammonium as the functional group.
 12. A method of fabricating a photoelectrochemical cell, the method comprising the steps of: (a) fabricating a photoanode comprising a photocatalyst; (b) fabricating a cathode; and (c) forming a solid polymer electrolyte layer comprising a solid polymer electrolyte between the photoanode and the cathode.
 13. The method of claim 12, wherein step (a) comprises the steps of: (a-1) applying a solution comprising a ruthenium precursor to a support comprising titanium dioxide; and (a-2) drying the support coated with the solution comprising the ruthenium precursor to fabricate the photoanode that comprises the support comprising titanium dioxide (TiO₂) and the photocatalyst comprising ruthenium oxide loaded on the support.
 14. The method of claim 13, wherein the ruthenium precursor comprises RuCl₃.
 15. The method of claim 12, wherein step (b) comprises the steps of (b-1) mixing a precursor of a compound represented by Structural Formula 1 below with a carbon material to prepare a mixed solution, and (b-2) drying the mixed solution to fabricate the cathode comprising the carbon material on which the compound represented by the Structural Formula 1 is loaded,

wherein in Structural Formula 1, R is a hydrogen atom, a carboxyl group, a sulfonic acid group, an amino group, or a hydroxyl group.
 16. The method of claim 12, wherein step (c) comprises the steps of: (c-1) positioning a proton exchange membrane comprising a cation exchange resin so as to face the photoanode; (c-2) positioning an anion exchange membrane comprising an anion exchange resin so as to face the cathode; and (c-3) positioning a polymer bead comprising the solid polymer electrolyte between the proton exchange membrane and the anion exchange membrane.
 17. A method of producing hydrogen peroxide, the method comprising the steps of: (1) providing a photoelectrochemical cell comprising a photoanode, a cathode, and a solid polymer electrolyte layer positioned between the photoanode and the cathode; (2) oxidizing water at the photoanode under light irradiation to generate electrons (e⁻), oxygen (O₂), and hydrogen ions (H⁺), and reacting the electrons (e⁻) with oxygen (O₂), and water at the cathode to generate active oxygen species and hydroxide ions (OH⁻); and (3) reacting the hydrogen ions (H⁺) with the active oxygen species in the solid polymer electrolyte layer to produce hydrogen peroxide (H₂O₂).
 18. The method of claim 17, wherein the active oxygen species comprise a hydroperoxyl radical (HO₂.⁻) and a superoxide radical (O₂.⁻).
 19. The method of claim 17, wherein the method produces hydrogen peroxide with electric energy generated from solar energy without requiring supply of external electric energy.
 20. The method of claim 17, further comprising the step of, after step (3), (4) adding water to the solid polymer electrolyte layer to dissolve the hydrogen peroxide to prepare an aqueous hydrogen peroxide solution, and discharging the prepared aqueous hydrogen peroxide solution from the solid polymer electrolyte layer to outside to obtain the aqueous hydrogen peroxide solution. 